Method of treating steel



4- A. R. STARGARDTER 7 1,948,192

IETHOD OF TREATING STEEL Filed larch 1 1932 Patented Feb. 20, 1934 UNITED STATES v 1,948,192 METHOD or TREATING STEEL Albert R. Stargardter, Brookline, Masa, assignor to Gillette Safety Razor Company, Boston, Mass., a corporation of Delaware Application March 10, 1932. Serial No. 597,945 11 Claims. (01. 148- 16) This invention relates to the treatment of steel for the purpose of imparting a blued finish to the surface thereof. It consists in a novel method characterized by the step of subjecting the heated steel to the action of an atmosphere having a controlled oxidizing effect. While the method is of general application it has a particular field of use in the treatment of strip steel, such for example, as that employed in the manufacture of safety razor blades and is herein disclosed as practised in that field.

A blued finish may be imparted to steel by hardening it and then drawing its temper to a point at which the steel is substantially softened. However, when so tempered, the steel is far too soft to serve as a satisfactory razor edge. Also soft steel may be blued by heating it to a definite temperature which is considerably below its critical point.

I have discovered that by subjecting steel under certain conditions to the action of an atmosphere having a controlled oxidizing effect, a blued finish may be imparted to it independently of hardness or temper. It is thus possible for the first time to produce steel articles of any desired degree of hardness having a blued surface finish of a character highly prized in cutting devices and other steel articles.

In carrying out the novel method of my invention, I preferably combine the coloring or blueing step with the heating of the steel preparatory to the hardening and tempering steps. Accordingly, in another aspect, my invention comprises a novel method of hardening and coloring steel 0 characterized by the steps of heating the steel to a temperature above its critical point, simultaneously subjecting it to the action of an atmosphere having a controlled oxidizing effect and then immediately hardening the colored or blued steel by chilling it. Preferably the steel is dry chilled between cooled plates since the appearance of the blued finish of the steel treated in such manner is superior to that of steel quenched in water or oil.

An important characteristic of the method of my invention consists in enveloping the steel being treated in a current of oxidizing gas which is heated above its ignition point, and in so confining and handling the gas current, that it is 0 conducted or directed away from the heated strip for complete combustion and allowed to burn only at a point remote therefrom. This is important as otherwise the lustre and appearance of the blued finish is impaired by the products of combustion.

It is proposed to control the oxidizing effect of the atmosphere to which the heated steel is subjected by varying the proportion of its constituents. Atmospheric oxygen and water vapor are both powerful oxidizing agents when heated and the presence of a regulated quantity of either or both of these gases in the mixture enveloping the steel is sufficient to ensure the continuity and integrity of the blued finish desired. By varying the relative quantities of the oxidizing constituents the tint or shade of the blued finish may be controlled and determined in accordance with the requirements of the work at hand, but in all cases the oxidizing effect of the gas mixture to which the steel is subjected is less than that of atmospheric oxygen, as otherwise, at the temperature I employ, the color of the steel would be carried beyond the blue.

The nature of my invention will be best understood and appreciated from the, following description of one manner in which it maybe carried out in connection with apparatus shown in the accompanying drawing, in which Fig. 1 is a view in perspective of a muflle which may be employed and its connections, showing two steel strips in passage therethrough;

Fig. 2 is a view in cross-section through the furnace chamber containing the muflle and,

Fig. 3 is a view in longitudinal section through the furnace chamber showing also the relation of the chilling and tempering devices to the furnace.

It will be understood that the illustrated apparatus represents one satisfactory form of equipment only and that the method of my invention is not restricted in its practice to this nor to any other specific form of apparatus.

As shown in the drawing, an elongated furnace is formed by walls 10 of refractory material and the furnace is provided with vents 12 in its upper wall near the discharge end thereof. Gas burners 14 are arranged at points along the sides of the furnace and by these the interior of the furnace is heated to the desired temperature. Preferably the burners are arranged so that the furnace presents to the strip steel passing through it, progressively hotter zones increasing in temperature toward its delivery end. The left-hand or inlet end of the furnace is closed by a plate 16 and the right-hand or delivery end by a corresponding plate 17.

Within the furnace chamber is enclosed an auxiliary muffle 18. This is closed at either end by the plates 16 and 17 of the furnace chamber and provided in its upper wall with an aperby an independent valve.

ture for a purpose presently to be described. The auxiliary mufile'18 is spaced at its sides and top from the corresponding walls of the furnace chamber and is heated by gas flames from the burners 14 which maintain the interior thereof at a high temperature defused without abrupt variations. Within the auxiliary muille 18 is mounted an elongated mufile 20, also closed at either end by the plates 16 and 17 and having adjacent to the delivery end of the furnace an upwardly-extending outlet duct 22 which passes through the aperture in the upper wall of the auxiliary mufiie 18. The mufile 20 is constructed of a heat-resistant alloy, such as nichrome, and its body is relatively shallow and flat with curved walls, being adapted to receive a strip of steel, or several strips arranged in horizontal position. Within the mufile 20, the plates 16 and 17 are provided with inlet and outlet slots through which pass the strips being treated. As herein shown, two strips 30 are guided in parallel paths, side by side, through the mufile.

At the inlet end of the mullle 20 is provided a supply pipe'28 and tothis are led an air inlet pipe 24 and a gas inlet pipe 26 each controlled The purpose of the supply pipe 28 is to conduct continuously to the mufile 20 gas of controllable oxidizing effect. Ordinary illuminating gas, which, as is well known, is reducing in its elfect, diluted with air has been found entirely satisfactory in practice. The addition of atmospheric oxygen to the reducing illuminating gas results in a mixture which is no longer reducing but slightly oxidizing in its effect at the temperature used. The mixture thus formed is admitted to the mufile 20 through the supply pipe 28 and may be adjusted as to its composition by properly setting the valves in the air and the gas pipes and by thus adjusting the mixture the tint of the blued ,finish may be varied and made lighter or darker. The gas so delivered to the mufile 20 envelops the steel strips and flows lengthwise along them until it reaches the upwardly-directed outlet duct 22 near the discharge end of the muffle. The gas current is at this point deflected upwardly away from the strip steel and passes out through the top of the auxiliary muflie 18. It will be understood that the mufile 20 is maintained at a temperature above the lower critical point of the steel being treated, for example, above 1400" F., and consequently the gas contained within the muffle is raised to a temperature considerably above its ignition point. Any substantialamount of the mixture is, however, prevented from burning within the muffie 20, partly on account of its velocity of fiow and partly on account of the restricted area of the muffle and of its discharge duct. The behavior of the oxidizing mixture within the muflle 20 is not entirely understood and it may be that its oxidizing effect is caused in part by conversion of reducing C0 of the illuminating gas to oxidizing CO2 in the mixture surrounding the steel strips. After leaving the duct 22, the oxidizing gas mixture is free to ignite and burn either within the furnace chamber or after it has passed upwardly through the duct 12 in the upper wall of the furnace chamber. In any case, the complete combustion of the gas takes place at a point remote from the strip steel being treated so that the latter is kept from contact with the products of this combustion.

The efiect of subjecting the steel to heat and the oxidizing eifect of the gas mixture is to produce upon its surface a smooth, uniform coat of blue oxide of attractive appearance. On passing out of the mufile 20' through the plate 17, the heated and blued strips 30 are guided at once between chilled plates 32 whereby the heated strips are hardened while the blued finish previously imparted to them is preserved.

Upon leaving the chilling platesv 32, the hardened and blued strips are at once guided to and between heated plates 34 by which the hardened strips may be drawn to any desired degree of tem- -per and this step also is carried out Without affecting the blued finish of the strips.

It will be noted that by the process above outlined, the color of the strips is imparted to them before the hardening operation is completed and entirely independently of the tempering operation. The color,'therefore, gives no indication of the temper of the strips but is imparted thereto by a novel sequence of steps which permit the steel to be subsequently treated and tempered to any desired degree. In manufacturing such articles as safety razor blades, the blued finish is highly prized and has been acquired heretofore only by methods involving the use of lacquer or the like, inasmuch as the temper corresponding to the usual blued finish is entirely too soft for razor blade construction. It will be observed that by my novel method, the process of manufacture is not lengthened or seriously complicated because the heating step, which is necessary in hardening the steel, is utilized also for the oxidizing step.

Having thus described my invention, what I claim as new and desire to secure by Letters Patent of the United States is:-

l. The method of producing colored and hardened strip steel, which consists in heating the strip to a temperature above its critical point, immersing the strip so heated in a gaseous mixture having a reducing constituent but being oxidizing in its effect, and then chilling the strip to harden it as thus oxidized.

2. The method of producing colored and hardened strip steel, which consists in heating the strip to a temperature approximating 1400" F., immersing the strip so heated in a mixture of heated air and CO, and then chilling the strip to harden it with the surface oxidation thus produced.

3. The method of hardening and uniformly coloring steel, which consists in heating it to a temperature at or above its hardening point, simultaneously subjecting it to the action of an atmosphere having a controlled oxidizing effect which is less than that of atmospheric oxygen, and then chilling it to produce a hardened and colored steel product.

4. The method of hardening and coloring steel, which consists in heating it to a temperature at or above its hardening point while exposed to an atmosphere having an oxidizing effect less than that of atmospheric oxygen, and then removing the steel from such atmosphere and at once chilling it, thereby producing a hardened and colored steel product.

5. The method of hardening and blueing strip steel, which consists in heating the strip to a temperature at or above its hardening point, meanwhile enveloping the heated strip in a moving current of oxidizing gas of less oxidizing effect than atmospheric oxygen, and thereafter chilling the strip, thereby producing a hardened and blued steel strip.

6. The method of hardening and uniformly blueing strip steel, which consists in progressively conducting it through successive heating zones, subjecting the heated strip in each zone to the action of a gas mixture of controlled oxidizing effect less than that of atmospheric oxygen, and then chilling the strip as it is removed from said oxidizing atmosphere, thereby producing a hardened and blued steel strip. A

7. The method of hardening and blueing strip steel, which consists in progressively heating successive zones in the strip to a temperature above its critical point, flowing a hot oxidizing gas along the heated strip and then directing the current thereof away from the strip,,and finally chilling the strip beyond'the point at which said current departs from it, thereby producing a hardened and blued steel strip.

8. The method, of hardening and blueing strip steel, which consists in passing the strip through an elongated furnace containing an oxidizing gas of less oxidizing effect than atmospheric oxygen, heating the furnace and the gas contained therein to a temperature above the lower critical point of the steel, and then chilling the strip progressively as it leaves the furnace, thereby producing a hardened and blued steel strip.

9. The method of coloring and hardening strip steel, which consists in flowing a current of oxidizing gas of less oxidizing effect than atmospheric oxygen along the strip, heating the gas to a temperature above its ignition point and above the critical point of the steel while it is in contact with the strip, controlling its flow in such manner that it burns only when out of contact with the strip, and chilling the steel strip.

10. The method of coloring and hardening strip steel, which.is characterized by the steps of flowing a current of oxidizing gas along the strip, heating the gas to a temperature above its ignition point and above the critical point of the steel while in contact with the strip, deflecting the current away from the strip and burning the gas only at points remote therefrom and finally chilling the steel to produce a hardened and blued strip.

11. The method of treating-strip steel, which is characterized by the steps of progressively heating successive zones in the strip to a temperature above the critical point of the steel, subjecting each zone as heated to the action of a gas mixture having a controlled oxidizing efiect which has less oxidizing effect than that of atmospheric oxygen, progressively chilling the strip as it leaves the oxidizing atmosphere, and subsequently heating the strip to temper it independently of the oxidized color imparted thereto.

' ALBERT R. STARGARDTER. 

